继承和多态之间的主要区别是什么？ [英] What is the main difference between Inheritance and Polymorphism?

问题描述

我在今天的模块开卷考试结束时遇到了这个问题，发现自己迷路了。我正在阅读 Head first Java ，两个定义似乎完全相同。我只是想知道主要的区别在于我自己的想法。我知道有很多类似的问题，但是，我没有看到哪些提供了明确的答案。

I was presented with this question in an end of module open book exam today and found myself lost. I was reading Head first Javaand both definitions seemed to be exactly the same. I was just wondering what the MAIN difference was for my own piece of mind. I know there are a number of similar questions to this but, none I have seen which provide a definitive answer.

推荐答案

继承是当阶级来自现有的阶级时。因此，如果你有一个 Person 类，那么你有一个 Student 类扩展 Person ，学生 继承 人所有的东西。您在Person中的字段/方法上放置的访问修饰符有一些细节，但这是基本的想法。例如，如果您在 Person 上有一个私有字段，那么 Student 将看不到它，因为它是私有的，私有的字段对于子类是不可见的。

Inheritance is when a 'class' derives from an existing 'class'. So if you have a Person class, then you have a Student class that extends Person, Student inherits all the things that Person has. There are some details around the access modifiers you put on the fields/methods in Person, but that's the basic idea. For example, if you have a private field on Person, Student won't see it because its private, and private fields are not visible to subclasses.

多态性处理程序如何决定应该使用哪种方法，具体取决于它具有什么类型的东西。如果您有一个 Person ，它有一个读取方法，并且您有一个 Student 扩展 Person ，它有自己的读取的实现，确定调用哪个方法由运行时为您服务，具体取决于您是否具有 Person 或 Student 。它有点棘手，但是如果你做了类似的事情

Polymorphism deals with how the program decides which methods it should use, depending on what type of thing it has. If you have a Person, which has a read method, and you have a Student which extends Person, which has its own implementation of read, which method gets called is determined for you by the runtime, depending if you have a Person or a Student. It gets a bit tricky, but if you do something like

Person p = new Student();
p.read();

调用学生上的读取方法。这就是多态性的作用。您可以执行该分配，因为 Student 是 Person ，但运行时很聪明足以知道 p 的实际类型是学生。

the read method on Student gets called. Thats the polymorphism in action. You can do that assignment because a Student is a Person, but the runtime is smart enough to know that the actual type of p is Student.

注意详情不同的语言。例如，你可以在javascript中继承，但它与它在Java中的工作方式完全不同。

Note that details differ among languages. You can do inheritance in javascript for example, but its completely different than the way it works in Java.

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